1. Field of the Invention
The present general inventive concept relates to an ink jet image forming apparatus capable of preventing a heater from overheating and damaging a print head when an error occurs in a system clock, and a method of controlling the same.
2. Description of the Related Art
An ink jet print head used in an ink jet image forming apparatus is able to eject droplets of ink onto a printing medium at a desired position so as to form an image.
The ink jet print head is generally divided into two types: a thermal driving type and a piezoelectric driving type, depending on the mechanism used to eject the ink droplets. The thermal driving type ink jet print head heats the ink contained in an ink chamber using heaters to generate bubbles in the ink, and then ejects the ink droplets in correspondence with a plurality of nozzles by the expansion force of the bubbles.
In such an ink jet image forming apparatus, a printer main body sends a signal for driving the heaters to the print head through serial communication, and a logic circuit formed in a head chip mounted in the print head controls the operation of the heaters to eject the ink droplets.
As illustrated in FIG. 1, a head chip HC1 of a print head includes an input data processor 10 which determines whether data received from a printer main body is printing data or common data so as to set up the status of the head chip, and processes the data. A heater controller 100 including a printing data processor 100a is provided to receive and process the printing data from the input data processor 10, and a heater driver 100b is provided to drive heaters so as to eject ink through the nozzles. A strobe signal generator 20 is used to count a serial clock received from the printer main body and to generate a strobe signal for driving the heaters, and an ink channel (not illustrated) is provided to contain the ink which is ejected through the plurality of nozzles by the pressure of the bubbles generated by the driving of the heaters.
The input data processor 10 divides the serial data into address ADDR and primitive data P_data, sends the address ADDR and primitive data P_data to the heater controller 100 if the serial data received from the printer main body through the serial communication is printing data, and analyzes the data and sets up a register of the strobe signal generator 20 and the head chip if the serial data is common data.
The strobe signal generator 20 counts the serial clock in synchronization with a load signal LOAD, generates a strobe pulse STRB for driving the heaters, and sends the strobe pulse to the heater controller 100.
The heater controller 100 includes the printing data processor 100a and the heater driver 100b to analyze the serial data received from the printer main body and to selectively drive the plurality of heaters.
Referring to FIG. 2, in order to simplify the system, the primitive data P_data and the address ADDR are transmitted through serial signal lines.
A reset signal RESET is applied to shift registers 103 and 106 and latch circuits 104 and 105. Thereafter, the shift registers 103 and 106 receive the primitive data P_data and the address ADDR in synchronization with the system clock SCLK, in order to select a nozzle corresponding to a certain heater.
The latch circuits 104 and 105 respectively latch the primitive data P_data and the address ADDR received from the shift registers 103 and 106 when receiving a load signal LOAD.
When the strobe pulse STRB is inputted to eject the ink through the nozzles, the latched signals are sent to a transistor (or a field effect transistor (FET)) of the corresponding nozzle through an AND gate 101 so as to turn on the transistor. A driving voltage Vph is applied to a thermal element of the heater corresponding to each nozzle, causing a driving current to flow in the heater, thereby ejecting the ink contained in the ink channel.
As illustrated in FIG. 3, when the load signal LOAD is inputted, the data is latched to the AND gate 101. The nozzles which eject the ink by a first strobe pulse STRB_1 become the nozzles corresponding to first data Data_1 and the nozzles which eject the ink by a second strobe pulse STRB_2 become the nozzles corresponding to second data Data_2. A time period when the current flows in the heater, that is, a heater driving time, is determined according to the pulse widths of the first strobe pulse STRB_1 and the second strobe pulse STRB_2.
As described above, the print head can receive the system clock SCLK, the serial data, the load signal LOAD and the reset signal RESET from the printer main body through the serial communication, in order to drive the heater.
Since the signal transmitted by the printer main body is transmitted in synchronization with the system clock SCLK, a head controller (not illustrated) of the printer main body to generate the system clock must include a complicated logic circuit so as to synchronize the timing of the signal.
If the printer main body is affected by electromagnetic interference due to reduction of electromagnetic susceptibility (EMS) during a printing operation, the printer main body is exposed to electrostatic discharge (ESD) such that latch-up of the system is caused, and abnormal operations are performed in the head controller of the printer main body, or connection failure occurs in a connector to connect a signal line between the printer main body and the print head. Thus, errors may occur in the system clock SCLK.
If the above-described abnormal phenomenon occurs in a process of counting the system clock SCLK received from the printer main body and generating the strobe pulse STRB for controlling the time period when the current flows in the heater, that is, if the system clock is stopped while the clock is counting, the system clock is continuously maintained at a low level as denoted by F1 of FIG. 4, and thus the strobe pulse STRB is continuously maintained at an enabled state. Thus, the heater is continuously driven for a long period of time and is damaged due to overheating of the heater. If the heater is damaged, the ink is not ejected through the nozzle corresponding thereto and thus print quality deteriorates.
To address this problem, a strobe pulse may be generated using a separate clock which is driven independent of the head controller of the printer main body. However, since the EMS should be considered, such methods are limited since the driving frequency of the separate clock should be lower than that of the system clock SCLK received from the printer main body. In addition, since the separate clock is not synchronized with the serial data and the system clock SCLK received from the printer main body, it is difficult to adjust the pulse width of the strobe pulse with high precision.
As described above, if the system clock is normal, the driving of the heater is performed in order to eject the ink. However, if an error occurs in the system clock due to ESD, the driving of the heater needs to be restricted, else the heater may be damaged.